1. Field of the Invention
The present invention relates to a method for retrofitting a pulverized coal boiler in which a pulverized coal boiler in an air combustion boiler system is retrofitted into a pulverized coal boiler in an oxyfuel combustion boiler system.
2. Description of Related Art
As part of measures against global warming, a method of burning a mixture gas of highly-pure oxygen and combustion exhaust gas instead of using conventional air has been proposed for burning fuel in a boiler. Hereinafter, this method is referred to as oxyfuel combustion, and a combustion method using air is referred to as air combustion.
Since the majority of exhaust gas will be CO2 in oxyfuel combustion, the exhaust gas does not require condensation for recovering CO2. The exhaust gas can be directly compressed and cooled to separate CO2 for liquefaction. This is one of the effective ways to reduce CO2 emissions. As a conventional oxyfuel combustion boiler system, as stated in Japanese Patent application Laid-open No. Hei 5 (1993)-26409, such an oxyfuel combustion boiler system has been known in which a two-stage combustion pulverized coal boiler having a burner and an after-air port is provided with an air separation unit and a CO2 recovering facility, and part of the combustion exhaust gas burnt in and exhausted from the pulverized coal boiler and combustion exhaust gas after CO2 has been recovered are recirculated and supplied to the pulverized coal boiler after being mixed with oxygen manufactured in the air separation unit, to be used as an oxidizing agent for fuel.
In addition, Japanese Patent application Laid-open No. 2001-201406 discloses a retrofit method for a pulverized coal boiler in an air combustion system. This discloses a technique in which an after-air port is installed obliquely upward at a position below the tip of the flame produced by a burner in a furnace, thereby allowing adjustments of the combustion load in the furnace.    Patent Document 1: Japanese Patent Application Laid-open No. Hei 5 (1993)-26409    Patent Document 2: Japanese Patent Application Laid-open No. 2001-201406